1. Field of the Invention
The present invention generally relates to portable rechargeable batteries and their construction. More particularly, the present invention relates to a portable rechargeable battery that has a user control for selecting the capacity that the battery can be charged to, and can subsequently discharge.
2. Description of the Related Art
In rechargeable batteries, such as lithium-ion batteries, the charge and discharge cycles have a dramatic impact on the life of the battery. In general, as the voltage charging the batteries increases, the initial capacity of the battery also increases, however the battery cycling life inversely decreases. As an example, if a standard 8 mm Li-ion battery that has a recommended charge voltage of 4.2V is charged to 4.3V, the added termination voltage increases the capacity of the battery between five an fifteen percent. The effect of overcharging the battery to achieve this increased capacity is that the cycle life of the battery is decreased 30-50%. Consequently, manufacturers set the internal charge level of rechargeable batteries to a level that creates a capacity that is effective for the application, but does not significantly adversely impact the battery cycle life.
Due to the manufacturer constraints on the preset charge capacity, the consumer does not have any ability to change the capacity of the battery. The charge level is controlled by the circuitry of the battery so that even a greater voltage applied at the input of the battery will not change the effective charging voltage to the cell. Moreover, batteries do not have an effective indicator to inform the user of the effective charge on the battery. Most batteries only have visual or audible indicators of the battery reaching a preset full-capacity charge. Without an effective indicator of the charge being applied, there is no way for the consumer to safely override the predetermined charge cycle.
Additionally, even if the consumer could increase the charge voltage, the consumer does not have the information regarding the true effective safe level of charging voltage and capacity of the battery in relation to the deleterious effects of the increased charging voltage on the battery life. A manufacturer would therefore be reluctant to allow the consumer to overcharge the battery and greatly shorten the battery life without fully informing the customer that their actions can shorten the battery life, and that any shortened cycle life is not due to a manufactured defect or other fault of the manufacturer.
Accordingly, it would be advantageous to have a rechargeable battery that can have the user set the capacity level that the battery is charged to, even though charging the battery to a high capacity adversely effects the battery""s functional life. It is thus to the provision of such an improved battery having a user control that allows the user to select the charge capacity of the battery that the present invention is primarily directed.